1. Technical Field
The subject invention relates generally to cooling systems for internal combustion engines of automotive vehicles and, more particularly, to an electromagnetically controlled thermostat valve for controlling the flow of liquid coolant to a radiator.
2. Description of the Related Art
An internal combustion engine that powers an automobile normally has a liquid cooling system for removing waste heat generated by the combustion process in the engine. Such a cooling system may comprise a pump operated by the engine, a radiator, and a thermostat valve. As the pump circulates liquid coolant through the system, engine heat is transferred to the coolant passing through engine coolant passages. When the engine has reached a predetermined operating temperature, the thermostat valve opens to allow coolant to flow through the radiator where heat is transferred from the coolant to ambient air passing across exterior surfaces of the radiator. Hence, the thermostat valve restricts coolant flow to the radiator until the engine heats the coolant to a temperature corresponding to the operating temperature of the engine. This allows a cold engine to reach the desired operating temperature more quickly. Once the thermostat valve has fully opened, the temperature of the coolant, and hence that of the engine, can fluctuate over a range of operating temperatures determined by various factors such as the size of the radiator, the rate at which the pump pumps liquid coolant through the radiator, how the engine is being operated, and the ambient air temperature. Should the operating temperature fall below this range, the thermostat valve will once again restrict flow to the radiator in an effort to restore the operating temperature of the engine.
Most thermostat valves have bimetallic coil or wax pellet type actuators. These valves are self-contained devices that open and close according to predetermined temperature limits. They have certain disadvantageous operating characteristics, including relatively slow response times and relatively wide switching hysteresis. Such characteristics result in a wide range of temperatures over which the valve operates between closed and open positions. Hence, such thermostats exhibit relatively loose temperature regulation. Furthermore, conventional thermostats do not allow optimal control over the cooling system because they passively respond to changes in coolant temperature only. Other factors, such as actual engine temperature, engine speed, coolant flow rate, and ambient air temperature cannot be utilized when setting the operating state of such thermostats.
Active thermal management control systems increase the fuel economy of automobiles, and use an electrically-controlled flow divider, or so-called proportional thermostat valve. Existing electromagnetic thermostat valves use linear actuators to replace wax pellets found in conventional thermostats. Although this design allows control by a central computer, the valve movement is against the fluid flow direction, just like in a conventional thermostat. Therefore, the linear actuator requires a constant power supply. Furthermore, the valve only has very a limited number of configurations, which are insufficient to achieve optimal and efficient operating conditions.
An example of a proportional coolant valve that is driven by a rotary actuator is disclosed by Busato et al in U.S. Pat. No. 5,950,576. The rotary actuator of this valve has to overcome a friction torque created by a coil spring against a moving element, and hence, also requires a constant power supply.
Another disadvantage arises with both types of valve systems when debris and impurities such as iron oxide, sand or scale is present in the coolant. The debris can cause clogging or potential seizure of two surfaces that move relative to one another.
The apparatus of the present invention addresses the need for a more rapid and effective control of coolant temperature than conventional systems. To obtain high cooling efficiencies, the thermostat valve according to one aspect of the invention is controlled via a central computer by monitoring other variables in addition to coolant temperature, such as engine block temperature, engine speed, coolant flow rate, and ambient air temperature. This control is achieved with a relatively simple mechanical device that affords complete control over the amount of coolant flow that reaches the radiator. Additional benefits include minimal power consumption to operate the valve, and the ability to independently control fluid flow to the radiator or bypass valves.
The apparatus of the present invention also addresses the need for a valve that is unaffected by the level of impurities in the coolant.